Method for controlling operation of ice-making machine

ABSTRACT

A method for controlling an operation of an ice-making machine configured to make ice by cooling a medium to be cooled, through heat exchange with a refrigerant. The method includes increasing an evaporation temperature of the refrigerant to be supplied to the ice-making machine when a drive current for an ice scraper of the ice-making machine is more than a first current value.

TECHNICAL FIELD

The present disclosure relates to a method for controlling an operation of an ice-making machine. More specifically, the present disclosure relates to a method for controlling an operation of an ice-making machine configured to make sherbet-like ice slurry.

BACKGROUND ART

Sherbet-like ice slurry has occasionally been used for refrigerating fish and the like. Heretofore, for example, a double pipe ice-making machine including an inner pipe and an outer pipe has been known as an apparatus for making such ice slurry (refer to, for example, Patent Literature 1). An ice-making system that includes such an ice-making machine also includes a tank for storing a medium to be cooled, such as seawater. The medium to be cooled is supplied from the tank to an inner pipe of the ice-making machine, and ice slurry is made through heat exchange of the medium to be cooled with a refrigerant supplied to an annular space between an outer pipe and the inner pipe of the ice-making machine. The ice slurry thus made is returned to the tank.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 3,888,789

SUMMARY Solution to Problem

A method for controlling an operation of an ice-making machine (hereinafter, also simply referred to as an “operation control method”) according to a first aspect of the present disclosure has the following configurations.

(1) A method for controlling an operation of an ice-making machine configured to make ice by cooling a medium to be cooled, through heat exchange with a refrigerant,

the method including:

increasing an evaporation temperature of the refrigerant to be supplied to the ice-making machine when a drive current for an ice scraper of the ice-making machine is more than a first current value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram of an exemplary ice-making system including an ice-making machine to which an operation control method according to the present disclosure is applied.

FIG. 2 is a side view of the ice-making machine illustrated in FIG. 1.

FIG. 3 is a sectional view of an ice scraper in the ice-making machine illustrated in FIG. 2.

FIG. 4 illustrates exemplary control on an evaporation temperature in an operation control method according to a first embodiment.

FIG. 5 is a graph of a behavior of a motor current in the operation control method according to the first embodiment.

FIG. 6 illustrates exemplary control on an evaporation temperature in an operation control method according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a specific description will be given of an operation control method according to the present disclosure with reference to the accompanying drawings. The present disclosure is not limited to the following exemplary description, and all changes that fall within metes and bounds of the claims, or equivalence such metes and bounds thereof are therefore intended to be embraced by the claims.

Ice-Making System

First, a description will be given of an exemplary ice-making system including an ice-making machine to which an operation control method according to the present disclosure is applied.

FIG. 1 is a schematic configuration diagram of an ice-making system A including an ice-making machine 1 to which the operation control method according to the present disclosure is applied. FIG. 2 is a side view of the ice-making machine 1 illustrated in FIG. 1. In the ice-making system A, the ice-making machine 1 continuously makes ice slurry from seawater (raw material) stored in a seawater tank (to be described later), and returns the ice slurry thus made to the seawater tank. The term “ice slurry” refers to sherbet-like ice in which fine ice is formed and suspended within water or a solution of water. The ice slurry is also called slurry ice, ice slurry, slurry ice, sluff ice, or liquid ice. The ice-making system A is capable of continuously making seawater-based ice slurry. The ice-making system A is therefore introduced in, for example, a fishing boat or a fishing port, and the ice slurry returned to the seawater tank is used for, for example, keeping fresh fish cool. In the illustrated ice-making system A, a resupply pump (not illustrated) resupplies new seawater to the seawater tank in accordance with an amount of the used (consumed) ice slurry.

The ice-making system A adopts seawater as a medium to be cooled. The ice-making system A also includes, in addition to the ice-making machine 1 serving as a part of a utilization-side heat exchanger, a compressor 2, a heat source-side heat exchanger 3, a four-way switching valve 4, a utilization-side expansion valve 5, a heat source-side expansion valve 6, a superheater 7, a receiver 8, a seawater tank (a reservoir tank) 9, and a pump 10. The ice-making machine 1, the compressor 2, the heat source-side heat exchanger 3, the four-way switching valve 4, the utilization-side expansion valve 5, the heat source-side expansion valve 6, the superheater 7, and the receiver 8 each serve as a part of a refrigeration apparatus. These apparatuses or members are interconnected via pipes to form a refrigerant circuit. The ice-making machine 1, the seawater tank 9, and the pump 10 are interconnected via pipes to form a seawater circuit. In the ice-making system A, each of the ice-making machine 1, the compressor 2, the heat source-side heat exchanger 3, the four-way switching valve 4, the utilization-side expansion valve 5, the heat source-side expansion valve 6, the superheater 7, the receiver 8, and the like is an equipment-side element, and each of the seawater tank 9, the pump 10, the pipes, and the like is a facility-side element.

The ice-making system A also includes a control apparatus 30. The control apparatus 30 includes a central processing unit (CPU) and a memory such as a random access memory (RAM) or a read only memory (ROM). The control apparatus 30 achieves various kinds of control concerning an operation of the ice-making system A, including the operation control according to the present disclosure, in such a manner that the CPU executes a computer program stored in the memory.

In a normal ice-making operation, the four-way switching valve 4 is maintained at a state indicated by a solid line in FIG. 1. The compressor 2 discharges a high-temperature and high-pressure gas refrigerant. The gas refrigerant flows into the heat source-side heat exchanger 3 that functions as a condenser, via the four-way switching valve 4. The heat source-side heat exchanger 3 condenses and liquefies the gas refrigerant by heat exchange with air provided by a fan 11. The liquefied refrigerant then flows into the utilization-side expansion valve 5 via the heat source-side expansion valve 6 in a fully open state and the receiver 8. The utilization-side expansion valve 5 decompresses the refrigerant to a predetermined low pressure. The low-pressure refrigerant then flows into an annular space 14 between an inner pipe 12 and an outer pipe 13 each serving as a part of an evaporator E of the ice-making machine 1, through a refrigerant inlet pipe to be described later.

In the annular space 14, the refrigerant evaporates by heat exchange with the seawater which the pump 10 supplies into the inner pipe 12. The seawater is cooled by the evaporation of the refrigerant. The seawater then returns to the seawater tank 8 via the inner pipe 12. The refrigerant gasifies by the evaporation in the ice-making machine 1. Thereafter, the refrigerant is sucked into the compressor 2. At this time, if the refrigerant that is not sufficiently evaporated in the ice-making machine 1 and slightly left liquefied is sucked into the compressor 2, an abrupt increase in pressure inside a compressor cylinder (liquid compression) or a decrease in viscosity of a refrigerating machine oil causes a failure in the compressor 2. In order to protect the compressor 2, the refrigerant from the ice-making machine 1 is heated by the superheater 7 before being sucked into the compressor 2. The superheater 7 is of a double pipe type. The refrigerant from the ice-making machine 1 is superheated when passing a space between an inner pipe and an outer pipe of the superheater 7. The refrigerant thus superheated then returns to the compressor 2.

If the flow of the seawater is stagnated in the inner pipe 12 of the ice-making machine 1, the ice is accumulated in the inner pipe 12 (ice accumulation) to hinder the operation of the ice-making machine 1. In this case, a defrosting operation (a heating operation) is performed for melting the ice in the inner pipe 12. At this time, the four-way switching valve 4 is maintained at a state indicated by a broken line in FIG. 1. The compressor 2 discharges the high-temperature and high-pressure gas refrigerant. The gas refrigerant flows into the annular space 14 between the inner pipe 12 and the outer pipe 13 of the ice-making machine 1 via the four-way switching valve 4. In the annular space 14, the gas refrigerant condenses and liquefies by heat exchange with the ice-containing seawater in the inner pipe 12. The liquefied refrigerant then flows into the heat source-side expansion valve 6 via the utilization-side expansion valve 5 in a fully open state and the receiver 8. The heat source-side expansion valve 6 decompresses the liquefied refrigerant to a predetermined low pressure. Thereafter, the refrigerant flows into the heat source-side heat exchanger 3 functioning as an evaporator. During the defrosting operation, in the heat source-side heat exchanger 3 functioning as an evaporator, the refrigerant gasifies by heat exchange with air provided by the fan 11. Thereafter, the refrigerant is sucked into the compressor 2.

The ice-making machine 1 is a portrait-oriented double pipe ice-making machine that includes the evaporator E including the inner pipe 12 and the outer pipe 13 whose axes extend horizontally, and an ice scraper to be described later. The evaporator E is of a flooded type, in which most of the annular space 14 between the inner pipe 12 and the outer pipe 13 is filled with the liquid refrigerant. The evaporator E thus enhances heat exchange efficiency of the refrigerant with the seawater. In addition, when most of the annular space 14 is filled with the liquid refrigerant, the refrigerating machine oil is easily discharged from the flooded-type evaporator. The refrigerating machine oil returns to the compressor 2 to compensate for unsatisfactory lubrication of the compressor 2, leading to improvement in reliability.

The inner pipe 12 is an element through which the seawater serving as a medium to be cooled passes. The inner pipe 12 is made of a metal material such as stainless steel or iron. The inner pipe 12 has a cylindrical shape, and is disposed in the outer pipe 13. The inner pipe 12 has two ends that are closed. In the inner pipe 12, the ice scraper 15 is disposed to scrape sherbet-like ice slurry off an inner peripheral face of the inner pipe 12 and to disperse the sherbet-like ice slurry in the inner pipe 12. The inner pipe 12 is connected at its first axial end (the right side in FIG. 2) to a seawater inlet pipe 16 through which the seawater is supplied into the inner pipe 12, and is also connected at its second axial end (the left side in FIG. 2) to a seawater outlet pipe 17 through which the seawater is discharged from the inner pipe 12.

The outer pipe 13 has a cylindrical shape, and is made of a metal material such as stainless steel or iron as in the inner pipe 12. The outer pipe 13 is connected at its lower side to a plurality of refrigerant inlet pipes 18 (three refrigerant inlet pipes 18 in FIG. 2), and is also connected at its upper side to a plurality of refrigerant outlet pipes 19 (two refrigerant outlet pipes 19 in FIG. 2). Each of the refrigerant inlet pipes 18 has on its upper end a refrigerant supply port 20 through which the refrigerant is supplied into the annular space 14. Each of the refrigerant outlet pipes 19 has on its lower end a refrigerant discharge port 21 through which the refrigerant is discharged from the annular space 14.

As illustrated in FIGS. 2 and 3, the ice scraper 15 includes a shaft 22, a support bar 23, a blade 24, and a motor 26. The shaft 22 has a second axial end that extends outward from a flange 25 on the second axial end of the inner pipe 12. The shaft 22 is connected at the second axial end to the motor 26 serving as a part of a drive unit for driving the shaft 22. The motor 26 is provided with an ammeter 31 that detects a drive current of the motor 26 and transmits the drive current to the control apparatus 30. The ice scraper 15 includes a plurality of the support bars 23 disposed upright on a peripheral face of shaft 22 at predetermined spacings, and a plurality of blades 24 respectively mounted to the distal ends of the support bars 23. Each of the blades 24 is, for example, a band plate-shaped member made of a synthetic resin. Each of the blades 24 has a tapered side edge directed forward in its rotational direction.

The annular space 14 is defined with an outer peripheral face of the inner pipe 12 and an inner peripheral face of the outer pipe 13 to form refrigerant paths that extend from the refrigerant supply ports 20 on the lower side of the outer pipe 13 to the refrigerant discharge ports 21 on the upper side of the outer pipe 13.

Operation Control Method

Next, a description will be given of a method for controlling an operation of the ice-making machine 1 in the ice-making system A. More specifically, a description will be given of an operation control method that involves changing operating conditions of the ice-making machine 1, stopping the ice-making machine 1, or restarting the ice-making machine 1, based on an ice packing factor in the seawater tank 9.

First Embodiment

In the ice-making system A, as the ice packing factor IPF in the seawater tank 9 increases through the operation of the ice-making machine 1, the amount of ice to be discharged from the seawater tank 9 increases, and the amount of ice in the inner pipe 12 of the ice-making machine 1 also increases. The increase in amount of ice in the inner pipe 12 causes an increase in driving torque of the motor 26 in the ice scraper 15 that scrapes the sherbet-like ice slurry off the inner peripheral face of the inner pipe 12. The increase in driving torque causes an increase in drive current of the motor 26. In the first embodiment, the operation of the ice-making machine 1 is controlled using a drive current value of the motor 26 in the ice scraper 15, the drive current value being detected by the ammeter 31 and transmitted to the control apparatus 30.

If the ice is excessively retained in the seawater tank 9 due to the increase in ice packing factor IPF of the seawater in the seawater tank 9, the seawater containing a large amount of ice flows into the ice-making machine 1, so that the current value of the motor 26 in the ice scraper 15 becomes larger than usual. In the first embodiment, when the current of the motor 26 exceeds a first current value, an evaporation temperature of the refrigerant to be supplied to the ice-making machine 1 is increased.

FIG. 4 illustrates exemplary control on the evaporation temperature in the operation control method according to the first embodiment. In FIG. 4, the vertical axis indicates a magnification of the evaporation temperature of the refrigerant in the evaporator E, that is, a ratio of the evaporation temperature to a normal evaporation temperature to be described later. In this control example, when the current value detected by the ammeter 31 is equal to or less than 6 A, the evaporation temperature is set at a normal set temperature t0 (e.g., −15° C.). In the first embodiment, when the current value exceeds the first current value, that is, 6 A, the evaporation temperature of the refrigerant to be supplied into the evaporator E is increased. More specifically, in the first embodiment, the evaporation temperature is set higher stepwise in accordance with an excess of the current. For example, when the current value is more than 6 A, but is equal to or less than 7 A, the operation is controlled to set the evaporation temperature 0.9 times as low as the normal evaporation temperature t0. In addition, when the current value is more than 7 A, but is equal to or less than 8 A, the operation is controlled to set the evaporation temperature 0.8 times as small as the normal evaporation temperature t0. The amount of ice made by the ice-making machine 1 is decreased in such a manner that the evaporation temperature is set higher than the normal value in accordance with the increase in current value.

In the first embodiment, when the current value exceeds a second current value (e.g., 11 A) larger than the first current value, a thermostat is forcibly turned off to stop the operation of the ice-making machine 1. In other words, the operation of the compressor 2 is stopped to stop the circulation of the refrigerant through the refrigerant circuit. It should be noted that the ice scraper 15 is continuously operated even when the thermostat is forcibly turned off. After the thermostat is forcibly turned off, when the current value of the motor 26 decreases to a certain value, for example, 9 A, the thermostat, which has been forcibly turned off, is turned on again to restart the operation of the compressor 2.

FIG. 5 is a graph of the behaviors of a current value in a case where the operation control according to the first embodiment is performed and the behaviors of a current value in a case where the operation control is not performed (the conventional art). In FIG. 5, the horizontal axis indicates a time (t), and the vertical axis indicates a current value (A) of the motor 26 in the ice scraper 15.

According to the conventional art, the operation control is not performed. Consequently, when the amount of ice in the inner pipe 12 exceeds a certain amount as the ice packing factor IPF increases with a lapse of a time, the drive current of the motor 26 sharply increases. Then, when the drive current exceeds a predetermined value A1, an overcurrent protective device is operated to stop the operation of the motor 26. In this case, since the motor 26 continuously operates at a high torque until the operation of the motor 26 is stopped, the blades 24, the support bars 23, and the like of the ice scraper 15 are possibly damaged.

The operation control according to the first embodiment is equal to that according to the conventional art in the current value of the motor 26 until the time t1 at which the amount of ice in the inner pipe 12 reaches a certain amount. According to the first embodiment, however, the current value of the motor 26 gradually increases after the time t1. Since the amount of ice is decreased in such a manner that the value of the evaporation temperature is set larger than usual in accordance with the increase in current value as described above, the increase in current value in the first embodiment is gentler than that in the conventional art.

When the current value of the motor 26 exceeds the second current value, that is, 11 A at the time t2, the thermostat is forcibly turned off to stop the operation of the ice-making machine 1. With this configuration, since ice is not newly made although the ice slurry in the seawater tank 9 is used, the amount of ice in the inner pipe 12 gradually decreases, and the drive current of the motor 26 also gradually decreases with this decrease. When the current value of the motor 26 falls below 9 A at a time t3, the thermostat, which has been forcibly turned off, is turned on again to restart the operation of the ice-making machine 1. The amount of ice in the inner pipe 12 increases again after the restart of the operation of the ice-making machine 1. When the current value of the motor 26 exceeds 11 A at a time t4, the thermostat is forcibly turned off again to stop the operation of the ice-making machine 1.

In the first embodiment, the operation of the ice-making machine 1 that is an equipment-side element is controlled based on the current value of the motor 26 of the ice scraper 15 in the ice-making machine 1. This configuration thus improves the reliability of operation control on the ice-making machine 1 irrespective of occurrence of, for example, abnormal communications with an equipment side in the conventional art. This configuration enables a reduction in risk of damage to the blades 24 and the support bars 23 of the ice scraper 15 due to ice made excessively, and improves the reliability of the ice-making system A as a system.

In the first embodiment, the evaporation temperature is increased stepwise in accordance with an excess of the current from the first current value. This configuration therefore enables stepwise reduction in amount of ice to be made by the ice-making machine 1.

Second Embodiment

In order to control the operation of the ice-making machine 1, a second embodiment focuses attention on an increase in pressure loss of the seawater flowing through the inner pipe 12 of the ice-making machine 1 from the inlet toward the outlet with an increase in amount of ice in the inner pipe 12. According to the second embodiment, specifically, the evaporation temperature of the refrigerant to be supplied to the ice-making machine 1 is increased when a pressure difference between a pressure of the seawater (the medium to be cooled) at the inlet of the ice-making machine 1 and a pressure of the seawater at the outlet of the ice-making machine 1 exceeds a first pressure value. In the second embodiment, a pressure sensor 32 detects a pressure of the seawater at the seawater inlet pipe 16 of the ice-making machine 1, and a pressure sensor 33 detects a pressure of the seawater at the seawater outlet pipe 17 of the ice-making machine 1 (see FIG. 2). The operation of the ice-making machine 1 is controlled using pressure values which the pressure sensors 32 and 33 transmit to the control apparatus 30.

FIG. 6 illustrates exemplary control on an evaporation temperature in the operation control method according to the second embodiment. In FIG. 6, the vertical axis indicates a magnification of the evaporation temperature of the refrigerant in the evaporator E, that is, a ratio of the evaporation temperature to a normal evaporation temperature to be described later. In this control example, the evaporation temperature is set at a normal set temperature t0 (e.g., −15° C.) during a period that the pressure difference between the pressure of the seawater at the seawater inlet pipe 16, the pressure being detected by the pressure sensor 32, and the pressure of the seawater at the seawater outlet pipe 17, the pressure being detected by the pressure sensor 33, is equal to or less than 0.03 MPa. In the second embodiment, when the pressure difference exceeds a first pressure value, that is, 0.03 MPa, the evaporation temperature of the refrigerant to be supplied into the evaporator E is increased. More specifically, in the second embodiment, the evaporation temperature is set higher stepwise in accordance with an excess of the pressure difference. For example, when the pressure difference is more than 0.03 MPa, but is equal to or less than 0.04 MPa, the operation is controlled to set the evaporation temperature 0.9 times as low as the normal evaporation temperature t0. In addition, when the pressure difference is more than 0.04 MPa, but is equal to or less than 0.05 MPa, the operation is controlled to set the evaporation temperature 0.8 times as low as the normal evaporation temperature t0. The amount of ice is decreased in such a manner that the evaporation temperature is set higher than the normal value in accordance with the increase in pressure difference.

In the second embodiment, when the pressure difference exceeds a second pressure value larger than the first pressure value, the thermostat is forcibly turned off to stop the operation of the ice-making machine 1. In other words, the operation of the compressor 2 is stopped to stop the circulation of the refrigerant through the refrigerant circuit. It should be noted that the ice scraper 15 is continuously operated even when the thermostat is forcibly turned off. After the thermostat is forcibly turned off, when the pressure difference decreases to a certain value, for example, 0.06 MPa, the thermostat, which has been forcibly turned off, is turned on again to restart the operation of the compressor 2.

According to the second embodiment, the operation of the ice-making machine 1 that is an equipment-side element is controlled based on the pressure difference between the pressure of the seawater (the medium to be cooled) at the seawater inlet pipe 16 of the ice-making machine 1 and the pressure of the seawater at the seawater outlet pipe 17 of the ice-making machine 1. This configuration thus improves the reliability of operation control on the ice-making machine 1 irrespective of occurrence of, for example, abnormal communications with an equipment side in the conventional art. This configuration enables a reduction in risk of damage to the blades 24 and the support bars 23 of the ice scraper 15 due to ice made excessively, and improves the reliability of the ice-making system A as a system.

In the second embodiment, the evaporation temperature is increased stepwise in accordance with an excess of the pressure difference from the first pressure value. This configuration therefore enables stepwise reduction in amount of ice to be made by the ice-making machine 1.

Other Modifications

The present disclosure is not limited to the foregoing embodiments, and various modifications may be made within the claims.

For example, in the foregoing embodiment (the first embodiment), the first current value of the motor and the second current value larger than the first current value are 6 A and 11 A, respectively. However, these current values are merely exemplary, and the present disclosure is not limited thereto. The first current value and the second current value are selectable as appropriate based on the size of the ice scraper, the characteristics of the motor, and others.

Likewise, in the foregoing embodiment (the second embodiment), the first pressure value and the second pressure value larger than the first pressure value are 0.03 MPa and 0.08 MPa, respectively. However, these pressure values are merely exemplary, and the present disclosure is not limited thereto. The first pressure value and the second pressure value are selectable as appropriate based on the size of the ice scraper, the characteristics of the pump, and others.

Moreover, in the foregoing embodiment (the first embodiment), when the current value of the motor decreases to 9 A, the thermostat, which has been forcibly turned off, is turned on again to restart the operation of the compressor. However, the current value at the time when the thermostat is turned on again is not limited thereto, and is selectable as appropriate based on the size of the ice scraper, the characteristics of the motor, and others.

Likewise, in the foregoing embodiment (the second embodiment), when the pressure difference between the pressures at the inlet and outlet of the ice-making machine decreases to 0.06 MPa, the thermostat, which has been forcibly turned off, is turned on again to restart the operation of the compressor. However, the pressure difference at the time when the thermostat is turned on again is not limited thereto, and is selectable as appropriate based on the size of the ice scraper, the characteristics of the pump, and others.

Moreover, in the foregoing embodiments, the evaporation temperature is increased stepwise in accordance with an excess of the current or the pressure difference. The evaporation temperature may alternatively be increased linearly in accordance with the excess. Also in the foregoing embodiments, the evaporation temperature is increased stepwise in accordance with an excess of the current or the pressure difference. The evaporation temperature may alternatively be increased by a preset temperature when the current or the pressure difference exceeds the first current value or the first pressure value.

Moreover, in the foregoing embodiment (the second embodiment), the pressure sensor 32 configured to detect a pressure of the seawater at the inlet of the ice-making machine 1 is disposed near the seawater inlet pipe 16. However, the pressure sensor 32 may be disposed at any location as long as it is capable of detecting a pressure of the seawater before heat exchange with the refrigerant in the evaporator E. For example, the pressure sensor 32 may be disposed at a position S1 indicated by a chain double-dashed line in FIG. 2 (inside the inner pipe 12). The same applies to the pressure sensor 33 configured to detect a pressure of the seawater at the outlet of the ice-making machine 1. The pressure sensor 33 may be disposed at a position S2 indicated by a chain double-dashed line in FIG. 2 (inside the inner pipe 12).

In the foregoing embodiments, the evaporator E is of a flooded type, in which most of the annular space 14 between the inner pipe 12 and the outer pipe 13 is filled with the liquid refrigerant. The evaporator E may alternatively be of a type, in which the refrigerant is jetted through a nozzle into the annular space 14 between the inner pipe 12 and the outer pipe 13.

EXPLANATION OF REFERENCES

1: ICE-MAKING MACHINE

2: COMPRESSOR

3: HEAT SOURCE-SIDE HEAT EXCHANGER

4: FOUR-WAY SWITCHING VALVE

5: UTILIZATION-SIDE EXPANSION VALVE

6: HEAT SOURCE-SIDE EXPANSION VALVE

7: SUPERHEATER

8: RECEIVER

9: SEAWATER TANK

10: PUMP

11: FAN

12: INNER PIPE

13: OUTER PIPE

14: ANNULAR SPACE

15: ICE SCRAPER

16: SEAWATER INLET PIPE

17: SEAWATER OUTLET PIPE

18: REFRIGERANT INLET PIPE

19: REFRIGERANT OUTLET PIPE

20: REFRIGERANT SUPPLY PORT

21: REFRIGERANT DISCHARGE PORT

22: SHAFT

23: SUPPORT BAR

24: BLADE

25: FLANGE

26: MOTOR

30: CONTROL APPARATUS

31: AMMETER

32: PRESSURE SENSOR

33: PRESSURE SENSOR

A: ICE-MAKING SYSTEM

E: EVAPORATOR 

1. A method for controlling an operation of an ice-making machine configured to make ice by cooling a medium to be cooled, through heat exchange with a refrigerant in a refrigerant circuit including a compressor, the method comprising: increasing an evaporation temperature of the refrigerant to be supplied to the ice-making machine when a drive current for an ice scraper of the ice-making machine is more than a first current value, stopping the operation of the compressor and continuing the operation of the ice scraper when the drive current is more than a second current value that is larger than the first current value, restarting the operation of the compressor when the drive current decreases to a predetermined value.
 2. The method according to claim 1, comprising: increasing the evaporation temperature stepwise in accordance with an excess of the current.
 3. (canceled)
 4. A method for controlling an operation of an ice-making machine configured to make ice by cooling a medium to be cooled, through heat exchange with a refrigerant in a refrigerant circuit including a compressor, the method comprising: increasing an evaporation temperature of the refrigerant to be supplied to the ice-making machine when a pressure difference between a pressure of the medium to be cooled at an inlet of the ice-making machine and a pressure of the medium to be cooled at an outlet of the ice-making machine is more than a first pressure value, stopping the operation of the compressor and continuing the operation of the ice scraper when the pressure difference is more than a second pressure value that is larger than the first pressure value, restarting the operation of the compressor when the pressure difference decreases to a predetermined value.
 5. The method according to claim 4, comprising: increasing the evaporation temperature stepwise in accordance with an excess of the pressure difference.
 6. (canceled) 